The invention relates generally to a component having multiple magnetic and nonmagnetic regions, and a method of forming the same. More particularly, the invention relates to a component having multiple magnetic and nonmagnetic regions, and formation of the same by nitriding.
The need for high power density and high efficiency electrical machines (i.e. electric motors and generators) has long been prevalent for a variety of applications, particularly for hybrid and/or electric vehicle traction applications. The current trend in hybrid/electric vehicle traction motor applications is to increase rotational speeds to increase the machine's power density, and hence reduce its mass and cost. However, it is recognized that when electrical machines are used for traction applications in hybrid/electric vehicles, there is a clear tradeoff between power density, efficiency, and the machine's constant power speed range—and that this tradeoff presents numerous design challenges.
The power density of an electric machine may be increased by increasing the machine size, improving thermal management, increasing rotor speed, or by increasing the magnetic utilization. The magnetic utilization may be increased by using a combination of processing and alloying of a rotor lamination to create a dual phase magnetic material by developing localized areas of high and low permeability. The localized areas of high and low permeability generally reduce flux losses during rotor operation.
A range of ferrous based soft magnetic compositions of the rotor lamination may be austenitized by a combination of processes to form regions of low permeability. This phase transformation at selected regions is normally thermally driven in the presence of carbides in the alloy. Upon local heating, the carbides that are present at selected locations dissolve in the matrix and depress the martensite start temperature, thereby aiding the stabilization of austenite regions at room temperature. However, the presence of carbides in a magnetic microstructure is known to increase coercivity and to lower the magnetic saturation, as compared to traditional ferrous-based magnetic steels. A different method of stabilizing the austenite phase at room temperature in intermediate regions of the soft magnet, while starting from a substantially single phase microstructure, is desired to decrease the coercivity. Embodiments of the present invention address these and other needs.